There are 2 models of the I-Charger. The standard model which can charge 3 x 2S batteries and the ECU model which can charge 2 x 2S and 1 x 3S battery. Both I-Chargers can charge both external balance and internal balance batteries.

You can add an additional 2S or 3S stack to either model:

You can add an additional 2S stack to the I-Charge 2 Charger so it would then charger 4 x 2S batteries

You can add an additional 3S stack to the I-Charge 2 Charger so you can then charge 3 x 2S batteries and 1 x 3S battery

You can add an additional 3S stack to the I-Charge ECU Charger so you can then charge 2 x 2S batteries and 2 x 3S batteries